1. Field of the Invention
The present invention generally relates to illuminating devices for use in display apparatuses such as liquid crystal televisions and the like. In particular, the present invention relates to an illuminating device having a fluorescent lamp, suitable for use in a display apparatus such as a liquid crystal television capable of high-speed moving image display, a display apparatus including the illuminating device, and a light-diffusing film used in the illuminating device.
2. Description of the Related Art
Fluorescent lamps are used in televisions and liquid crystal displays (LCDs) for personal computers (PCs). Typically, phosphors that respectively emit three types of light, i.e., blue light, green light, and red light (more than three types of light may be used depending on the type of display), are applied in the fluorescent lamp. The display colors of a LCD are usually produced by allowing white light emitted from a backlight, e.g., a fluorescent lamp (cold cathode fluorescent lamp (CCFL)), a hot cathode fluorescent lamp (HCFL), an external electrode fluorescent lamp (EEFL), a flat fluorescent lamp (FFL), or the like, to pass through blue, green, and red color filters.
In order to improve the performance of the LCD, various investigations have been conducted on liquid crystal materials, light-emitting diodes (LEDs) as the light sources for the backlights, fluorescent lamps, phosphors, driving systems, luminance degradation, color reproducibility, enlargement of color gamut, moving image display quality, and the like. For example, the moving image display quality has been improved by employing a 120 Hz drive or by employing a pseudo impulse display mode in which a liquid crystal having a high-speed response characteristic is used and in which a black-insertion technique and a blinking backlight technique are combined (e.g., refer to Special Report: Image Information Media Annual Report (Tokushu Eizo Joho Media Nenpo), Kurita et al., The Institute of Image Information and Television Engineers, Vol. 60, No. 8, pp. 1169 to 1177 (2006) (LCD, p. 1169 right column to p. 1172 left column), and High Imaging Quality based on Optically Compensated Bend Mode Liquid Crystal Technology, Takimoto et al., Toshiba Review, Vol. 60, No. 7, pp. 42 to 45 (2005) (Moving Image Quality Improving Technology (p. 44, left column to p. 45 left column, and FIGS. 6 to 9)).
The existing technology related to color quality of an illuminating device that uses a fluorescent lamp will now be described.
Japanese Unexamined Patent Application Publication No. 4-370650 (“'650 document” hereinafter) (paragraph 0009 to 0011, FIGS. 1 and 2) titled Color Sequential Illumination System contains following descriptions.
FIG. 11A is a schematic view of an embodiment of a lamp used in the color sequential illumination system according to '650 document and FIG. 11B is a cross-sectional view taken along line XIB-XIB in FIG. 11A. FIGS. 11A and 11B are FIGS. 1 and 2 of the '650 document, respectively.
Referring to FIGS. 11A and 11B, reference numeral 101 indicates illumination means such as a discharge lamp. This illumination means includes a glass envelope 102 the inside surface of which is coated with a blue phosphor material 104 in the form of a powder. The ends of the envelope 102 are sealed and contain electrodes 106 for exciting a discharge, for example an ultra-violet discharge, within a gas 108 contained within the glass envelope 102.
Around the outside of the glass envelope 102 is a dye-doped organic fluorescent material in the form of a plastics material. In operation of the illumination means, the discharge in the gas 108 causes generation of light within the glass envelope 102. This causes the blue phosphor powder 104 to emit blue light which in turn stimulates fluorescence within the fluorescent plastics material 110. In this case, the fluorescent plastics material 110 is chosen so as to have a color characteristic of a suitable wavelength, for example green or red.
Because the optical decay time of the organic fluorescent material 110 is substantially equivalent to that of the blue phosphor powder 104 (approximately 0.04 ms), the light emissions of both colors will no longer occur for a significant time after the illumination means has been switched off. Furthermore, since the decay times of blue, green and red light can be arranged to be substantially equal, the light emitted from a color sequential illumination system can be fully synchronized with the electrical signals used to control energisation of the lamps and a reduction in unwanted color mixing will result. The plastics material and the fluorescent dyes used to produce the organic fluorescent material 110 can degrade with prolonged exposure to relatively high levels of ultra-violet radiation, such as those arising from the discharge excited in the envelope 102. However, because the envelope 102 is constructed from glass, there is no need to filter out ultra-violet radiation as glass is a good absorber of such radiation.
Japanese Unexamined Patent Application Publication No. 10-69889 ('889 document) (paragraphs 0013 to 0016, FIG. 1) titled Variable Color Fluorescent Lamp contains following descriptions.
FIG. 12 is a schematic diagram showing one embodiment of a variable color fluorescent lamp according to '889 document. FIG. 12 is FIG. 1 in '889 document.
FIG. 12 shows a variable color fluorescent lamp of one embodiment that includes an outer tube 201, an inner tube 202, inner tube supporting plates 203, and electrodes 204a, 204b, 205a, and 205b. 
The outer tube 201 is composed of, for example, glass, which is a light-transmitting member and has a shape of a cylinder having an inner diameter of about 30 mm and a length of about 1200 mm. A phosphor having a color temperature of 2800 K (not shown) is coated on the inner surface of the outer tube 201. The two ends of the outer tube 201 are sealed with end plates 206a and 206b, and the electrodes 204a and 205a are provided to the end plate 206a and the electrodes 204b and 205b are provided to the end plate 206b. An inert gas and a metal vapor, i.e., a mercury vapor, of several torrs are hermetically enclosed in the space inside the outer tube 201.
The inner tube 202 is composed of glass, i.e., a light-transmitting material, as with the outer tube 201. The inner tube 202 has a spiral shape and installed inside the outer tube 201. The inner tube 202 is obtained by processing a cylindrical member having an outer diameter of 12 mm into a spiral structure having a turn inner diameter of 5 mm and a length per turn of 150 mm. A blue green phosphor (not shown) having a chromaticity of (0.248, 0.346) is applied on the inner surface and a phosphor having a color temperature of 2800 K, which is the same as that of the phosphor applied on the outer tube 201, is applied on the outer surface. Furthermore, a pair of electrodes 205a and 205b are installed near the two ends inside the inner tube 202. The inner tube 202 is fixed to the inner tube supporting plates 203 so that the low points of the spiral structure abut the inner surface of the outer tube 201 every turn. Note that the space inside the inner tube 202 is arranged to form the same hermetically sealed space as that inside the outer tube 201.
The color variable fluorescent lamp having the above-described configuration has the outer tube 201 and the inner tube 202 lighted in parallel to each other via a light-control device (not shown) and controlled independently so that light of a desired color can be obtained. In this embodiment, a color temperature of 2800 K was obtained by lighting only the outer tube 201 and a color temperature of 6000 K was obtained by lighting both the outer tube 201 and the inner tube 202.
The physical explanation regarding the decay time of the phosphors is given in, for example, Phosphor Handbook edited by Keikotai Dou Gakkai and published by Ohmsha Ltd., first edition, pp. 65 to 66 (1987).
With regard to phosphor sheets, Japanese Unexamined Patent Application Publication Nos. 2007-86797 (paragraph 0065 to 0070 and 0077 to 0078), 2006-126109 (paragraph 0157), 2004-161808 (paragraphs 0067 to 0068, FIG. 1), and 2008-50593 (paragraphs 0006 to 0010, 0066, and 0085 to 0086, FIG. 3) provide descriptions.